Arthropods have occupied various habitats on Earth. What structural features were of greatest importance

Arthropods have occupied various habitats on Earth. What structural features were of greatest importance in their wide distribution in nature?

1) chitinous cover – external skeleton, protection;
2) articulated limbs and their modification;
3) development of various respiratory organs (gills, pulmonary sacs, trachea);
4) complication of the nervous system, complex instinctive behavior and development of the sense organs.

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